Blitz... you're really not one to be talking about people's density
I can't think of any reason why not, other than that April Fool's joke. Thwacked me good, it did. Er, and it thwacked most of the hosted projects, too. Any admin who particpated in that thing has no right to speak of anyone else's density.

Nebula-wise, couldn't this be done by reducing the number of nebula poofs? Or would this just leave holes in the nebula?
Edit: Got an idea! Would it be possible to, on select nebula missions, replace the motion debris with large poofs, the density of which could easily be edited via a program such as Paint Shop Pro? Oh! And then, we convert them from 2D spirites to actual 3D models, creating a hyper-realistic nebula-enviroment!
And the RAM to support all this will be delivered via flying pigs!